It is known that ring-opening polymerization of a cycloolefin containing norbornene moiety, e.g. dicyclopentadiene (called "DCP" hereinafter) in the presence of a metathesis polymerization catalyst system produces a cross-linked polymer containing olefinic groups on the main chain (e.g. Japanese Patent Laid Open Sho 58-129013). In such known technique, there are easily obtained large-sized molded articles of the cross-linked polymers by reaction molding process from DCP. The molded articles have been taken notice from the industrial point of view since they have attractive physical properties as balanced in stiffness and impact resistance. On the other hand, some of 5-alkylidenebicyclo[2.2.1]hept-2-enes (called "ABH" hereinbelow) by the formula ##STR2## wherein R' and R" independently represent hydrogen atom or a lower alkyl group, both R' and R" not being hydrogen at the same time, are available. For example, 5-ethylidenebicyclo[2.2.1]hept-2-ene (called "ENB" hereinbelow) among them, is obtained by isomerization of 5-vinylcyclo[2.2.1]hept-2-ene (called "VBH" hereinbelow) which is a Diels-Alder adduct of cyclopentadiene and butadiene. ENB is advantageously used as the third component for ethylenepropylene-diene rubber and is commercially available in such a purity as can be applied to ionic polymerization.
Further, Diels-Alder addition of cyclopentadiene to the above-mentioned ABH yields a corresponding 6-alkylidene-1,4,5,8-dimethano-1,4,4a,5,7,8,8a-heptahydronaphthalene (called "ADHN" hereinbelow) of the formula ##STR3## wherein R' and R" are as defined above.
As obvious from the above-mentioned chemical formulas, ABH and ADHN both have one acyclic olefinic group in addition to the cyclic olefinic group.
It is also known that the acyclic olefin, when added to the metathesis polymerization system of a cyclic olefin, participates in the reaction and acts as a chainterminator or a chain-transfer agent.
Therefore, it would be duly considered that when ABH and ADHN would be used in metathesis polymerization, said acyclic olefinic group present should act as a chain-terminator in the metathesis polymerization to form rather low-molecular-weight cross-linked metathesis polymers, and volatile by-products.
In fact, it was reported that 5-methylidenbicyclo[2.2.1]hept-2-ene (called "MBH" hereinafter), corresponding to the case of R'=R"=H in the general formula above, had yielded a mostly cross-linked polymer in the presence of the metathesis catalysts [Paul R. Hein J. Polymer Sci., Polym. Chem. 11, 167(1973)]. Analogously, as mentioned in the Comparative Examples 2-3 later, we have tested the metathesis homopolymerization of VBH and MBH respectively, both resulting in a soft, fragile, insoluble polymer containing many irregular voids. This is a clear evidence of the involvement of the pendant acyclic olefinic group in the metathesis reaction as a chain-terminating or chain-transfer group.
In contrast, we have found that ENB, a typical example of ABH, yields a rigid, tough, soluble polymer having substantially no void in the metathesis polymerization. This different behavior of ENB in the metathesis polymerization from VBH and MBH is quite unexpected, since the structures of the three are very analogous. The difference between ENB and VBH lies only in the position of the acyclic olefinic bond, while the difference between ENB and MBH is that the former has a methyl substitute to the methylidene group of MBH. In summation, both MBH and VBH have an .alpha.-olefinic group as a pendant acyclic group, but ENB has an inner olefinic group substituted with three hydrocarbon groups. Therefore, said different behavior of ENB in the metathesis polymerization can be explained only by substantially no participation of the substituted olefinic group of ENB in the metathesis polymerization due to steric hindrance.
We have also found that a typical ADHN, 6-ethylidene-1,4,5,8-dimethano-1,4,4a,5,7,8,8a-heptahydronaphthalene (called "EDHN" hereinafter), which is the Diels-Alder adducts of ENB with cyclopentadiene, shows similar behaviors to that of ENB. In addition, we have found that such ABH and ADHN as ENB and EDHN can be applied to reaction molding method to form molded articles of attractive properties and that especially when they are used with other metathesispolymerizable monomers, e.g. DCP, much improvement as mentioned in details later can be achieved to the reaction molding process and molded articles therefrom.
Now, we have found that, when ABH and/or ADHN is used as at least a part of monomers for the metathesis polymerization, the acyclic pendant olefinic group of ABH or ADHN, which is substituted by at least three hydrocarbon groups, hardly participate in the metathesis polymerization and does not do any harm, and thus, the ring-opening polymerization of the norbornene-type cyclic olefin predominantly occurs to produce a tough high-molecular weight polymer having pendant acyclic olefinic groups.
We have also found that ABH and/or ADHN can be advantageously applied to the reaction molding process as at least a part of monomers with such metathesis polymerization monomers as DCP.
Therefore, it is an object of the present invention to provide new polymers by metathesis polymerization of ABH or ADHN. A further object is to provide useful molded articles from said polymers. Another object of the invention is to provide processes for preparing said new polymers and said useful molded articles. A further object is to provide polymerizable compositions therefor.